Unsettled Derby Week Weather

Okay all, hope you enjoyed the warm and dry weather that the last week or so, because wetter changes in store.

Here's the set up, a frontal boundary will oscillate from near the Ohio River to the lower Great Lakes region the next 4 days. In addition, weak upper disturbances will move through the southwesterly flow aloft providing for lifting of this airmass that will be quite moist and relatively unstable. The bottom line... occasional shower and thunderstorms will occur across the Ohio Valley the rest of this week.

It still looks like there MAY be a window of dry weather to get much of Oaks in relatively dry but it will be close ! The front mentioned above will finally get a good kick southeast through the region Friday night as a strong shortwave moves across the Great Lakes area. Timing is everything when it comes to the Derby Festival, Oaks, and Derby day itself and hopefully the rain will hold off until later Friday night when the front is expected to finally move through and until the Oaks day activities are done.
Derby day morning, the front is expected to be well south. The rain should be done or ending with drier weather returning for Derby day afternoon...

Hey, you know it had to happen... it's difficult to get 2 full weeks of sunny, warm, and dry weather - especially this time of the year (let alone anytime of the year).

We'll keep you updated...
Jay

Improvements On The Way...

The upper level system that brought the scattered showers and isolated pockets of small hail to the region earlier today is now showing signs of lifting to the northeast allowing for rising heights and an overall warming to the atmosphere. By week's end, ridging will be in place in both the upper and lower parts of the atmosphere and with H85 temps warming to levels of +14 to +16 C, surface temperatures are still expected to climb into the low and mid 80s Friday and continue through the weekend...

Okay lots of talk about the type of precip that occurred with the showers earlier today... We here at WLKY-TV believe that we had mainly small hail and not sleet. Sleet typically starts off as a snowflake that melts into a raindrop as it falls through a warm layer (above 0 C) aloft then refreezes into an ice pellet - provided the layer of cold air beneath the warm / melting layer is deep enough for refreezing to occur. If the low level cold layer is not sufficiently thick, the raindrop will not refreeze but instead fall to the surface as a supercooled raindrop and freeze on contact if sfc temperatures are below freezing - freezing rain.
Today's weather featured a very well-mixed atmosphere - steep lapse rates (very nearly dry adiabatically) from almost 800mb to the surface with a positive area (CAPE) from about 900mb to 650mb. This was enough to kick off convective showers (updrafts) which "lifted" some of the raindrops back into the cloud where temperatures were below critical. As a result these raindrops froze into little chunks of ice (small hail). But because the CAPE was quite small, updraft strength was also relatively weak and not able to suspend anything more than these very small hailstones. This is why we believe it was indeed a small hail event and NOT sleet as others have claimed.

One More Blahh Day... Then "It's About Time !!!!!"

A deep upper level trough - with plenty of cold air aloft, will continue to dominate the region today... model progged soundings show a deep and well mixed low layer and some positive area as well. Simply put... a gusty day expected with clouds filling in and showers developing. H85 temps would suggest low / mid 50s for max temps.

Cold upper trough moves east later tonight and tomorrow setting us up for a huge warming trend later in the week. Each and every day, H85 temps will warm and so will the max afternoon readings. By Friday, the mid range models were progging +14 to + 16C air !! That easily translates to low / mid 80s. This warm pattern will hold on through the weekend with dry weather also expected. The bottom line, the weather should be beautiful for all the Derby festival events and opening day at Churchill this weekend.

Next week.... things start to get a little more fuzzy but overall it looks like the pattern will stay mild to warm as the main northern jet branch stays well north. Having said that, a southern stream shortwave may play havoc with the Oaks & Derby day weather. Of course timing is everything - especially this time of the year and we'll watch it for you real close. Enjoy the warmer weather (after today) ... it looks great !

Jay

A Beautiful Thunder On The Way !!

High pressure in both the upper and lower parts of the atmosphere will bring us beauitful weather for the end of this work week and the start of the weekend. Bottom line... it looks like a beautiful Thunder Over Louisville is on the way this go around. Expect lots of sunshine and warming temperatures for Friday followed by a few high clouds Saturday afternoon and Saturday evening - but rain is NOT expected !! Temperatures on Saturday afternoon will climb into the 70s and drop back into the 60s for the fireworks show beginning at 9:30 pm .
Showers and storms will enter the picture for Sunday as an upper low "opens up" and begins pushing east into the Ohio Valley but until that time... enjoy !!!!!!!!!!


Jay

Unsettled End To The Work Week

Another, in a series, of upper level systems will eject towards the Ohio River Valley the next 24 to 36 hours. As this potent upper system approaches, strong WAA will set up over the area later tonight into early Friday morning. A strengthening LLJ (as much as 65 kts) will advect moisture and warm air into the Ohio Valley. Low level convergence along and north of the sfc warm frontal boundary will lead to a growing area of showers and storms later Thursday night into early Friday morning. The most concentrated activity will occur on the elevated front which will be located near the Ohio River and points north. Freezing levels around H7 indicate that some of the stronger cells will have the potential to produce some hail.

The WAA precip will lift north of our area Friday morning leaving us with a brief lull in the convective activity. A second round of showers and storms will occur as the sfc low pressure system and its attendant cold front sweep the area Friday afternoon. CAPEs are progged to be as high as 2000 near the KY-TN border to 1000 J/kg near the Ohio River and then rapidly fall off north of the river. The problem... shear !!! check out the 0 to 6k shear 18z Friday... not too impressive near the Ohio river but it does increase as you head south. Typically 30kts of shear is sufficient for organized storm structure... we're flirting with that , at least near the Ohio river, Friday afternoon as the second round of convection is expected.

So, bottom line... Showers and storms later tonight and very early Friday. These storms will be elevated in nature but do pose a hail threat especially with the stronger convective elements. Another round of shower and storms Friday afternoon. Some of these storms also have a threat to become severe with wind and hail being the primary threats - although an isolated tornado will be possible closer to the warm frontal boundary and sfc low track where low level veering could lead to localized increased values of SRH. The better tornado threat will likely occur farther south through the TN valley and deep south later Friday afternoon as this is the area that will see moderate to strong instability, increasing 0 to 1 and 0 to 3k helicities, and increasing shear values all in the same basic area. SPC convective outlook for Friday looks really good to me at this point.

Have a great day,

Jay